Each arrow is the word "why" which is used to challenge a concept in order to see whether it is the only way of doing things.

2. Why does a plate have to be round? A girl was asked to design a new plate, so she challenged the idea of "roundness" and as a result she designed a plate that was long and narrow and stretched out toward the middle of the table - when you finished eating at one end you turned it round and started at the other.